The present invention provides a semiconductor device, and more particularly, relates to a light emitting device with roughened surface that increases external quantum efficiency of the device.
For a light emitting device that uses solid-state materials, the light emitting efficiency is determined by the internal together with external quantum efficiency. Generally, the internal quantum efficiency highly relates to materials per se and the epitaxy quality; and the external quantum efficiency highly relates to refractive index of the materials and surface flatness. The refractive index of AlInGaN series materials is about between 2.2 and 2.9. The external quantum efficiency of an AlInGaN series light emitting chip without surface treatment is about 10% to 20%. The overall light emitting output will be significantly improved if the external quantum efficiency is enhanced.
So far, the surface roughening operation according to prior art is performed after the stage of epitaxy growth. For example, in U.S. Pat. No. 5,040,044, a surface of an LED device is roughened by the chemical etching to reduce overall reflection and to increase light output. Other related prior arts include U.S. Pat. Nos. 5,898,191 and 5,429,954. However, the above prior art process treatment is not suitable for GaN series materials since they are rigid and corrosion-resistant over acids and bases. Ordinary chemical agents and organic solvents are hard to etch the GaN series materials. A reactive ion etching (RIE) method that is mostly applied to etch GaN will deteriorate the quality of epitaxial layers. Particularly, the p-type GaN epitaxial layers are susceptible to increase in resistance and becomes an insulator.
In consideration of the above recitations, the present invention provides a AlGaInN series light emitting device with high output luminance by directly growing a rough surface using epitaxial technology.
Comparing to light emitting devices that do not apply the techniques of the present invention, the luminance of light emitting devices of the present invention significantly increases.
In order to further depict the ways, structures and features of the present invention, the following drawings in conjunction in details of invention describing the embodiments of the present invention are provided.